This is a continuing long-term project in which a large number of non-diabetic relatives of diabetic patients, as well as asymptomatic mildly diabetic patients, are being studied periodically. In addition to detecting early defects in carbohydrate metabolism, we are seeking to find parameters, other than those associated with carbohydrate metabolism, which will indicate the existence of the early diabetic states. Methods by which the evolution from prediabetes to subclinical diabetes, from subclinical diabetes to latent chemical diabetes, and from latent asymptomatic diabetes to overt diabetes can be modified, are being sought. Young patients with latent (asymptomatic or chemical) diabetes have been studied prospectively for periods of up to 23 years and will continue to be studied to ascertain possible changes in (1) carbohydrate metabolism, (2) insulin secretion, (3) glucagon secretion, (4) growth hormone secretion and (5) the possible evolution of microangiopathy, macroangiopathy and neuropathy. BIBLIOGRAPHIC REFERENCES: Fajans, S. S., Floyd, J.C., Jr., Tattersall, R.B., Williamson, J.R., Pek, S., and Taylor, C.I.: The Various Faces of Diabetes in the Young. Arch. Int. Med. 136:194-202, 1976. Fajans, S.S.: The Natural History of Idiopathic Diabetes Mellitus. Heterogeneity of Insulin Responses in Latent Diseases. In: The Genetics of Diabetes Mellitus, Creutzfeldt, W., Kobberling, J. and Neel, J. V., eds. Springer-Verlag, Heidelberg, Chapter 8, pp. 64-78, 1976.